1. Technical Field
The present invention relates in general to disk drives and, in particular, to an improved system, method, and apparatus for a protective means for minimizing the damage done to recorded data in a disk drive due to stray magnetic fields.
2. Description of the Related Art
Data access and storage systems generally comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one or more disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand rpms. Hard disk drives have several different typical standard sizes or formats, covering server, desktop, mobile, and consumer electronics applications.
A typical HDD also uses an actuator assembly to move magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
A slider is typically formed with an aerodynamic pattern of air bearing surfaces that enable the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each disk and flies just over the disk's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a rigid actuator arm that supports the entire head flying unit. Several rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
The disk is mounted and clamped to a hub of a motor. The hub provides a disk mounting surface and a means to attach an additional part or parts to clamp the disk to the hub. In most typical motor configurations of HDDs, the rotating part of the motor is attached to or is an integral part of the hub. The rotor includes a ring-shaped magnet with alternating north/south poles arranged radially and a ferrous metal backing. The magnet interacts with the motor's stator by means of magnetic forces. Magnetic fields and resulting magnetic forces are induced via the electric current in the coiled wire of the motor stator. The ferrous metal backing of the rotor acts as a magnetic return path. For smooth and proper operation of the motor, the rotor magnet magnetic pole pattern should not be substantially altered after it is magnetically charged during the motor's manufacturing process.
Unfortunately, the data recorded in a disk drive can be erased when exposed to high stray magnetic fields, especially during a writing operation. Coercivity (measured in Oersteds, Oe) is a property of magnetic material and is defined as the strength of magnetic field necessary to reduce the magnetization in the material to zero. The higher the coercivity, the harder it is to erase data from a medium. The concern of stray field data erasure is increased with perpendicular recording technology. Some configurations permit data to be erased by a stray magnetic field as low as 25 Oe. Thus, an improved means for protecting drives by minimizing the damage done to recorded data in a disk drive due to stray magnetic fields would be desirable.